1. Field of the Invention
This invention relates to an actuator.
2. Prior Art
Shape memory alloy has a characteristic that if its predetermined shape is set at a predetermined high temperature region, for example, 60xc2x0 C. and its shape is memorized in advance, it is transformed into the memorized shape when the shape memory alloy is heated to cause its temperature to exceed a transformation temperature, for example, 60xc2x0 C., even if the shape is transformed into a shape different from the memorized shape at a normal temperature region which is lower than the predetermined high temperature, for example, 20xc2x0 C.
There is provided an actuator in which an acting member is of shape memory alloy under utilization of this characteristic. This actuator is constructed such that the acting member is formed by a wire of shape memory alloy, for example, and a predetermined first shape, for example, a shrunk shape is memorized in the acting member at a predetermined high temperature region. Then, at the normal temperature region which is lower than this temperature range, an external force is applied to the acting member with a spring and the like to transform it into a second shape different from the first shape, for example, an extended shape, a driven member is connected to the acting member and the driven member is set at a second position.
Under this condition, when the acting member of shape memory alloy is heated more than a transformation temperature, the acting member is transformed from the aforesaid second shape, i.e. the extended shape to a memorized first shape, i.e. the shrunk shape and transformed, and the driven member connected to the acting member can be moved from the second position to the first position.
Then, when the aforesaid acting member of shape memory alloy is cooled to its normal temperature, the acting member is transformed again into a second shape, i.e. a stretched shape with an external force, a force of spring and the like, the driven member connected to the acting member can be moved from the first position to the second position, i.e. its initial position.
FIGS. 21 and 22 show one example of an actuator provided with the acting member of shape memory alloy, wherein this is an example in which the actuator is applied to a mechanism for engaging with or releasing a charge lever for a camera and the like. FIG. 21 indicates an initial state in which the actuator is not operated and the charge lever is held and FIG. 22 indicates a state in which the actuator is operated and the charge lever is released.
In FIGS. 21 and 22, reference numeral 101 denotes an engaging lever, reference numeral 102 denotes an acting member of shape memory alloy and this acting member is a wire of shape memory alloy. Reference numeral 104 denotes a spring for retracting the engaging lever 101, reference numeral 106 denotes a charge lever and reference numeral 107 denotes a running spring for retracting the charge lever 106.
The wire 102 of shape memory alloy is made such that its one end is fixed to a pin 101a of an engaging lever 101 and the other end is fixed to a fixed pin 102a arranged on a fixing member such as a frame not shown. To both ends of the wire of shape memory alloy are connected a switch SW and a power supply BA in series. When the switch SW is closed, an electrical current is flowed from the power supply BA to the wire 102 of shape memory alloy and heat is generated by a resistance of the wire itself. It is assumed that a predetermined shrunk shape is memorized in advance in the wire 102 of shape memory alloy.
The engaging lever 101 is rotatably supported around a shaft 103 and biased to rotate in a clockwise direction by a spring 104 suspended between the fixed pin 104a on the fixed member and a pin 104b, and it is abutted against a stopper pin 105 and stopped there.
To the charge lever 106 is fixed one end 107a of the running lever 107, and the other end 107b of the running spring 107 is fixed to the fixed member 109. The charge lever 106 is moved in a leftward direction as viewed in FIG. a 21 by a charge mechanism not shown under its initial state, engaged with an engaging claw 101c at the extremity end of the engaging lever 101 and it is held at the position shown in FIG. 21. In this state, the running spring 107 is biased.
When the switch SW is turned on, an electrical current is flowed from the power supply BA to generate heat and when its temperature is increased by more than a transformation temperature, the wire 102 of shape memory alloy is transformed into a predetermined shrunk shape memorized in it against a biasing force of the spring 104.
With such an arrangement as above, since the engaging lever 101 is turned in a counterclockwise direction around the shaft 103 and the engaging claw 101c of the engaging lever 101 is disengaged from the charge lever 106 as shown in FIG. 22, the charge lever 106 is moved in a rightward direction in FIG. 21 by a biasing force of the running spring 107 to perform some predetermined operations such as a spring-up of a mirror in a single-lens reflex camera, an exposure starting operation, opening or closing of a film cartridge lid, and a pop-up of a flash light emitting device, for example, and then it is abutted against the stopper pin 108 and stopped there.
When the switch SW is turned off to shut off a supplying of electrical current to the wire 102 of shape memory alloy, the wire 102 of shape memory alloy is cooled. The engaging lever 101 is turned in clockwise direction around the shaft 103 by a biasing force of the spring 104 and the engaging claw 101c at its extremity end is returned back to a position where it can be engaged.
In turn, the charge lever 106 is moved again in a leftward direction as viewed in FIG. 22 by a charge mechanism not shown, engaged with the engaging claw 101c at the extremity end of the engaging lever 101, returned back to its initial state shown in FIG. 21 and at the same time the running spring 107 is biased.
The actuator applied with shape memory alloy described above has some features such as a simple structure, light weight and easy control and then it can be applied to various kinds of devices.
However, it has been found that the actuator applied with the shape memory alloy has two problems to be solved which will be described as follows.
The first problem consists in the fact that if an ambient temperature becomes more than a transformation temperature of shape memory alloy even in the case that it is not necessary to operate the actuator, the acting member is transformed to its memorized shape and performs a non-intended operation. Then, as long as the actuator is set at ambient temperature more than the transformation temperature of shape memory alloy, there occurs a disadvantage that the transformed state of the acting member to the memorized shape is continued to be kept.
The second problem is a fact that a close relation is kept among a stress caused by a spring and the like applied to the shape memory alloy, and a transformation starting temperature and its life, and a high stress enables a transformation starting temperature to be increased, but a life of the acting member becomes short under a high stress.
That is, if a high tension is applied to the acting member in such a way that the actuator may not be erroneously operated within a wide operating temperature range and a high stress is generated, a life of the acting member becomes short, and in turn if the tension applied to the acting member is reduced to attain a sufficient life time, and the stress is set to be low, there occurs a disadvantage that the operable temperature range not performing any malfunction is made narrow and an operating temperature range required for the actuator can not be assured.
It is an object of the present invention to provide an actuator applied with a new shape memory alloy solving the problems without damaging superior characteristics found in the shape memory alloy.
It is a major object of the present invention to provide an actuator applied with a new shape memory alloy which can be operated within a wide operating temperature range and has a long life time.
It is another object of the present invention to provide an actuator applied with a new shape memory alloy in which a malfunction generated when an ambient temperature becomes more than a transformation temperature of shape memory alloy is prevented and its operating temperature range is assured to be wide.
It is a still further object of the present invention to provide an actuator applied with a new shape memory alloy in which a value of stress applied to the acting member is adjusted in response to an ambient temperature, a value of stress is set to be low at a low temperature range and a value of stress is set to be high at a high temperature range to cause the operating temperature range to be wide.
It is a yet further object of the present invention to provide an actuator applied with a new shape memory alloy in which an operation caused by the acting member is made null and an occurrence of malfunction not intended can be prevented in advance even if the acting member of shape memory alloy is transformed to its memorized shape when the ambient temperature becomes more than a transformation temperature of shape memory alloy.
Other objects of the present invention will become apparent from the detailed description of the present invention in reference to the drawings.